This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Kenan & Kel
There's zero proof that Chris's mother is alive beyond his mere sayings. Kenan explicitly states that he never has met her despite almost daily reference from his boss and all of Chris's domicile photos lack any viewing of her; one would consider this an oddity since they are roommates. Worse, Chris's fish is named "Norman", ala the fictional serial killer famous for murdering and subsequently inhabiting his mother's life..
The special Two Heads Are Better Than None movie. It was much darker than what is normally seen, including actual murders.
The dinner they had was implied to be a person since it was never specified what type meat it was. This leads to Fridge Horror since Kel was the only one enjoying it.
The severed heads in the basement, which leads to some dark humor as Kel talks to them before realizing they're dead.